Roofing and the like



Patented Nov. 4, 1941 ITE-lo smr ROOFING AND ree LIKE Richard A. 'Wilkins, Rome, assignor-to Revere Copper and Brass Incorporateiltome,

N. Y., acorporationof Maryland 7 Application March .4, 1941,

No Drawing.

Serial No. 381,698

" ,iclaims. (01.108713) My invention relates to roofing and the like, and particularly to improvements in the roofing forming the subject matter of my pending applications'Ser-ial Number 363,515, filed October 30, 1940, now Patent 2,240,447, and Serial Number 381,697, filed March 4', 1941, nowPatent 2,244,093.

As pointed out in the above mentionedpending applications, the material heretofore commonly employed for copper'roofing, sheathing-and other exposed protective coverings for buildings has been thinrolled sheets of highly refined copper.

Further, in refining copper for these purposes it has heretofore always been the practice of producers thereof to remove so far as possible all impurities soas to secure as pme a copper as possible. The known highresistance of pure cop'- f per generally to chemical corrosion, and theo bfif served fact that impurities commonly foundjinf rolled copper tend to makeit'less ductile inboth;

the hot and cold rolled conditions,,more diffi cult to produce by either ;hot orcold rol1ing,ar 1d, ommonly cold short.'in'the sense that it tends to crack when bent, or otherwise cold worked, have Caused u e c p e re o or t e o sidered the most satisfactory' commercially availablernaterial for light weightmetalroofing and theliker In fact duringthe past forty years coppenroofing' has for these reasons been made almost exclusively .of electrolytically refined copper, whichcommonly is 999% "pure copper. I

, Nevertheless 'itis ,a frequently observed I act that copper roofing, ,even ,when substantially 1.00% pureelectrolytically refined copper, often fails in use, being subject to cracking sufiicient'torender it non-waterproof. Heretofore it was believed that these cracks were caused .by mechanical fatigueresulting by reason ofthe cyclicstresses set-upby alternate expansion andcontraction of v o, andtheman f lur w i ctua lyhave o curred in spite of these precautions, have seriously interfered with the general adoption of this otherwise very satisfactory roofing. I

As pointed outin applicants pending applications above referred to, applicant'has found that" the failure of copper roofing and :the. like heretofore hasnot been correctlyunderstood; This material, he has found, does not fail primarily by reason of the cyclic stresses to which it is subjected-when in use, as heretofore believed, but,

strangely enough, primarily by reason of a here tofore wholly unsuspected type of corrosion which occurs when this highly pure copper is exposed to qan atmosphere contaminated by wind home products of combustion'of modern domestic and industrial fuel burning appliances and industrial atmospheres in general. I

Applicant has found, that upon removing pitted,- instead of being in its smooth unpitted condition in which it originally left the'rolling I millfor the metalshowing auniform decrease in' thickness over its whole surface dueto corrosion.

His-"investigations show that these pits" are caused by the formation on the copper, when' exposed'to' a contaminated atmosphere, of a of corrosion products which is characterized by a lack of adhesion to the copper, a lack of tenacity in respect to failure, and a tendency toward perviousness which allow the copper to .be attacked locally rather than uniformly by the corrosive ,media and thereby result in the formation of sharply defined, inwardly pointed pits in the nature of ,notches. He has found that copper so attacked rapidly fails when subjected to the cyclic stresses hereinbefore referred to by reason of the natural tendency of the stresses to be concentrated in the metal below the bottoms of the notch-like pits. As a result of thisv concentration of the stresses, themetalbelow the bottoms of the pits ,work hardens and the fatigue strength of the material is exceeded, and as a result the metal I cracks at the pits.

.Pure copper roofing applicant has found is comparatively sensitive to this notch effect, when caused by a combination of chemicalcorrosion and subjection to cyclic stresses, onaccount'of the film which forms on it causing the pure copper to pit and the great sensitivity of pure copper to work hardening when cold worked.

"The above mentioned application Serial Number 363,515 points out that this type of failure of copper roofing as constructed from thin sheets, commonly from 0.003 to 0.03 inch in thickness, can be substantially entirely avoided by incorporating into,the copper controlled amounts of arsenic, while the other application points out that the patina and other accumulated corrosion products copper roofing which'has failed, the copper" roof ng surface thus exposed is characteristically this can be done by incorporating into the copper controlled amounts of antimony.

When either arsenic or antimony is incorporated it has been found that the surface of the copper, after the patina or other accumulated products of corrosion are removed, is in an unpitted condition, any corrosion which has occurred being substantially uniformly distributed over its surface. Also it has been found that either arsenic or antimony most markedly decreases the sensitivity of the copper to work hardening when cold worked, and therefore any scratches, dents, or the like in the nature of notches which might be formed during the handling or installation of the roofing will not cause.

it to fail by notch effect. In other words, the action of either arsenic or antimony is twofold: it prevents notches from being formed by corrosion and prevents the roofing failing by notch effect even if the notches are accidentally formed by mechanical means.

It has been found that the presence of the proper amount of arsenic or antimony in the copper roofing produces on the roofing surface a corrosion film which is tenacious, adherent, impervious and non-hygroscopic, the film being comparably as ductile as the copper base material itself, thus permitting the roofing to be repeatedly bent without rupture of the film or interruption of its adherence to the copper. Thus this film effectively protects the underlying base material from contaminated air and moisture, and in this 'way effectively eliminates the possibility of the formation of the above mentioned notchlike pits, for any slight amount of corrosion which occurs will be uniformly distributed over the surface of the copper. Most importantly this film has the property of being self-healing in the sense that if for any reason its continuity is locally interrupted it will substantially immediately reform when subjected to corrosion and thus act to prevent substantial local corrosion at the interrupted regions which in a pure copper would continue to corrode at an accelerated rate resulting in pitting at the point of interruption of the film.

The above mentioned application Serial Number 363,515 points out that the beneficial effects of arsenic in copper roofing are obtained with additions of 0.02 to 1.5% arsenic, the maximum beneficial effects being secured with about 0.5%. The other application points out that the beneficial effects of antimony in copper roofing are obtained with additions of 0.05 to 0.08% antimony, the degree of the effect produced being approximately directly proportional to the amount of antimony. In each case substantially the same effect is produced. except that with antimony a stronger roofing in respect to tensile strength may be secured than with arsenic. Applicant has now found that increased effects can be secured by addingto the copper controlled amounts of both arsenic and antimony particularly if these substances are properly proportioned relative to each other. It has been found that these increased effects are secured by adding 0.1 to 0.8% arsenic and 0.05 to 0.4% antimony with the amount of arsenic in each instance preferably at least twice the amount of antimony, the maximum effects being secured with about 0.5% arsenic and 0.25% antimony, say in the range of 0.4 to 0.6% arsenic and 0.2 to 0.3% antimony.

The effect of these specified combinations of arsenic and antimony is to produce on the copper mentioned for the binary alloys.

roofing surface a self-healing, corrosion film, apparently formed of a complex arsenic-antimony oxide, which is much more tenacious, adherent, and impervious than the film formed when only arsenic or only antimony is added. The insensitivityof the roofing to work hardening and notch effect is substantially the same when both arsenic and antimony are added and the amount of arsenic is at least twice the amount of antimony as when either alone is added within the ranges of arsenic and antimony However, because of the improved effect in respect to the protective properties of the film formed when both arsenic and antimony are added, additions of both of them secure a roofing that has a greater durability or overall fatigue strength when subjected, to the combined effects of corrosion and cyclic stresses than roofing having either arsenic or antimony alone.

When the amount of arsenic is at least twice the amount of antimony within the ranges of arsenic and antimony specified for additions of the two the roofing can be fabricated by rolling with substantially the same ease as commercially pure copper. Increasing the amount ofantimony in excess of one-half the amount of arsenic however tends somewhat to increase the difiiculty in fabricating the copper into roofing sheets by hot or cold rolling, and causes in some instances the roofing sheets to have less ductility and less resistance to work hardening and notch effect than if the amount of antimony wereless than onehalf the amount of arsenic.

When adding either arsenic or antimony best results ordinarily will be secured if the roofing does not contain impurities which tend to render it less malleable in the hotand cold conditions and thus tend to cause the hot or cold rolling or other working of the roofing during its fabrication to result in sub-microscopic surface cracks therein analogous in their effects to pits.

Among these deleterious substances are lead, bismuth, iron, nickel and sulphur, very small amounts of all of which tend to make the copper roofing more difficult to produce, and all of which tend to make the copper roofing containing both arsenic and antimony approach the poor resistance of pure copper roofing to corrosion and its sensitivity to notch effect, and thereby act to destroy the beneficial effects of the combination of arsenic and antimony. The presence of such substances as cobalt, tin, silicon and zinc in substantial amounts had also best be avoided as they tend to increase the sensitivity of the copper roofing to work hardening and notch effect. Thus it will be understood, that in the sense the copper roofing does not contain deleterious substances or amounts thereof which substantially destroy the beneficial effects tended to be imparted by the combination of arsenic and antimony, the balance of the alloy aside from the arsenic and antimony is essentially copper.

In making the roofing according to the invention the copper may be melted,andthe arsenic and antimony added to the melt in the form of binary copper-arsenic and copper-antimony alloys rich in arsenic and antimony, respectively. The molten metal may then be cast into slabs, which latter may be rolled into sheets of desired thickness by the usual mill process of rolling copper roofing sheets. Finally the rolled sheets are annealed to the degree of softness that will best resist the cyclic stresses to which they are subjected when in use.

For convenience in terminology the article of manufacture according to the invention is termed roofing, it being understood that as used in the appended claims such term includes various shingles, sheathings, valleys, and like protective coverings for buildings, as well as what in a more limited sense is ordinarily termed roofing. Also it will be understood that the roofing according to the invention comprises sheet copper presenting an extensive external roofing surface, and may in this sense consist of a backing having an exterior sheet of copper as well as consist Wholly of sheet copper.

I claim:

1. Roofing comprising sheet copper presenting an extensive external roofing surface, the copper being alloyed with such amounts of arsenic and antimony between 0.1 and 0.8% arsenic and 0.05 and 0.4% antimony as will cause the formation on said surface when exposed to atmospheric corrosion of a self-healing, adherent, protective film composed predominantly of compound containing arsenic and antimony, while rendering the sheet copper less sensitive to failure by reason of notch effect than sheet copper without the arsenic and antimony when subjected to the cyclic stresses caused by expansion and contraction of the roofing.

2. Roofing comprising sheet copper presenting an extensive external roofing surface, the copper being alloyed with approximately 0.1 to 0.8% arsenic and 0.05 to 0.4% antimony, the balance of the alloy in respect to the arsenic and antimony being essentially copper.

3. Roofing comprising sheet copper presenting an extensive external roofing surface, the copper being alloyed with approximately 0.1 to 0.8% arthe alloy in respect to the arsenic and antimony being essentially copper.

RICHARD A. WILKINS. 

